Molded chip fabrication method and apparatus

ABSTRACT

A method and apparatus for coating a plurality of semiconductor devices that is particularly adapted to coating LEDs with a coating material containing conversion particles. One method according to the invention comprises providing a mold with a formation cavity. A plurality of semiconductor devices are mounted within the mold formation cavity and a curable coating material is injected or otherwise introduced into the mold to fill the mold formation cavity and at least partially cover the semiconductor devices. The coating material is cured so that the semiconductor devices are at least partially embedded in the cured coating material. The cured coating material with the embedded semiconductor devices is removed from the formation cavity. The semiconductor devices are separated so that each is at least partially covered by a layer of the cured coating material. One embodiment of an apparatus according to the invention for coating a plurality of semiconductor devices comprises a mold housing having a formation cavity arranged to hold semiconductor devices. The formation cavity is also arranged so that a curable coating material can be injected into and fills the formation cavity to at least partially covering the semiconductor devices.

This application is a continuation of, and claims the benefit of, U.S.patent application Ser. No. 10/666,399, filed on Sep. 18, 2003 now U.S.Pat. No. 7,915,085.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to coating of semiconductor devices and moreparticularly to a method and apparatus for coating light emitting diodes(LEDs) with a matrix material containing one or more light conversionmaterials.

2. Description of the Related Art

LEDs are solid-state devices that convert electric energy to light andthey generally comprise an active layer of semiconductor materialsandwiched between two oppositely doped layers. When a bias is appliedacross the doped layers, holes and electrons are injected into theactive layer where they recombine to generate light that is emittedomnidirectionally from the active layer and from all surfaces of theLED. Recent advances in LEDs (such as Group III nitride based LEDs) haveresulted in highly efficient light sources that surpass the efficiencyof filament-based light sources, providing light with equal or greaterbrightness in relation to input power.

One disadvantage of conventional LEDs used for lighting applications isthat they cannot generate white light from their active layers. One wayto produce white light from conventional LEDs is to combine differentwavelengths of light from different LEDs. For example, white light canbe produced by combining the light from red, green and blue emittingLEDs, or combining the light from blue and yellow LEDs.

One disadvantage of this approach is that it requires the use ofmultiple LEDs to produce a single color of light, increasing the overallcost and complexity. The different colors of light are also generatedfrom different types of LEDs fabricated from different material systems.Combining different LED types to form a white lamp can require costlyfabrication techniques and can require complex control circuitry sinceeach device may have different electrical requirements and may behavedifferently under varied operating conditions (e.g. with temperature,current or time).

More recently, the light from a single blue emitting LED has beenconverted to white light by coating the LED with a yellow phosphor,polymer or dye, with a typical phosphor being cerium-doped yttriumaluminum garnet (Ce:YAG). [See Nichia Corp. white LED, Part No.NSPW300BS, NSPW312BS, etc.; See also U.S. Pat. No. 5,959,316 to Hayden,“Multiple Encapsulation of Phosphor-LED Devices”]. The surroundingphosphor material “downconverts” the wavelength of some of the LED'sblue light, changing its color to yellow. For example, if anitride-based blue emitting LED is surrounded by a yellow phosphor, someof the blue light passes through the phosphor without being changedwhile a substantial portion of the light is downconverted to yellow. TheLED emits both blue and yellow light, which combine to provide a whitelight.

One conventional method for coating an LED with a phosphor layerutilizes a syringe or nozzle for injecting a phosphor containing epoxyover the LED. One disadvantage of this method is that it is oftendifficult to control the phosphor layer's geometry and thickness. As aresult, light emitting from the LED at different angles can pass throughdifferent amounts of conversion material, which can result in an LEDwith non-uniform color temperature as a function of viewing angle.Another disadvantage of the syringe method is that because the geometryand thickness is hard to control, it is difficult to consistentlyreproduce LEDs with the same or similar emission characteristics.

Another conventional method for coating an LED is by stencil printing,which is described in European Patent Application EP 1198016 A2 toLowery. Multiple light emitting semiconductor devices are arranged on asubstrate with a desired distance between adjacent LEDs. The stencil isprovided having openings that align with the LEDs, with the holes beingslightly larger than the LEDs and the stencil being thicker than theLEDs. A stencil is positioned on the substrate with each of the LEDslocated within a respective opening in the stencil. A composition isthen deposited in the stencil openings, covering the LEDs, with atypical composition being a phosphor in a silicone polymer that can becured by heat or light. After the holes are filled, the stencil isremoved from the substrate and the stenciling composition is cured to asolid state.

One disadvantage of this method is that, like the syringe method above,it can be difficult to control the geometry and layer thickness of thephosphor containing polymer. The stenciling composition may not fullyfill the stencil opening such that the resulting layer is not uniform.The phosphor containing composition can also stick to the stencilopening which reduces the amount of composition remaining on the LED.These problems can result in LEDs having non-uniform color temperatureand LEDs that are difficult to consistently reproduce with the same orsimilar emission characteristics.

Another conventional method for coating LEDs with a phosphor utilizeselectrophoretic deposition. The conversion material particles aresuspended in an electrolyte based solution. A plurality of LEDs arearranged on a conductive substrate that is then almost completelyimmersed in the electrolyte solution. One electrode from a power sourceis coupled to the conductive substrate at a location that is notimmersed in the solution, and the other electrode is arranged in theelectrolyte solution. The bias from the power source is applied acrossthe electrodes, which causes current to pass through the solution to thesubstrate and its LEDs. This creates an electric field that causes theconversion material to be drawn to the LEDs, covering the LEDs with theconversion material.

One of the disadvantages of this method is that after the LEDs arecovered by the conversion material, the substrate is removed from theelectrolyte solution so that LEDs and their conversion material can becovered by a protective epoxy. This adds an additional step to theprocess and the conversion material (phosphor particles) can bedisturbed prior to the application of the epoxy. Another disadvantage ofthis process is that the electric field in the electrolyte solution canvary such that different concentrations of conversion material can bedeposited across the LEDs. The conversion particles can also settle inthe solution which can also result in different conversion materialconcentrations across the LEDs. The electrolyte solution can be stirredto prevent settling, but this presents the danger of disturbing theparticles already on the LEDs.

SUMMARY OF THE INVENTION

The present invention seeks to provide a method and apparatus forcoating semiconductor devices wherein the geometry and thickness of thecoating layer can be controlled. The methods and apparatus according tothe present invention are particularly adapted to coating light emittingdiodes (LEDs) with a controlled layer of “matrix material” havingconversion particles. The methods and apparatus are simple and easy touse, and allow for the reproduction of coated semiconductor deviceshaving coating layer geometry and thickness that are substantially thesame.

One embodiment of a method for coating a plurality of semiconductordevices according to the present invention comprises providing a moldwith a formation cavity. A plurality of semiconductor devices aremounted within the mold formation cavity and a coating material isinjected into the mold to fill the mold formation cavity and at leastpartially cover the semiconductor devices. The coating material is curedor otherwise treated so that the semiconductor devices are at leastpartially embedded in the coating material. The cured coating materialwith the embedded semiconductor devices is removed from the formationcavity. The semiconductor devices are separated so that each is at leastpartially covered by a layer of the coating material.

Another embodiment of a method according to the present invention isparticularly adapted to coating a plurality of light emitting diodes(LEDs) and comprises providing a mold with a formation cavity. Aplurality of LEDs are mounted within the mold formation cavity and amatrix material is injected or otherwise introduced into the mold tofill the formation cavity and at least partially cover the LEDs. Thematrix material is then cured or otherwise treated so that the LEDs areat least partially embedded in the matrix material. The matrix materialwith the embedded LEDs is removed from the formation cavity and theembedded LEDs are separated so that each is at least partially coveredby a layer of the matrix material.

One embodiment of an apparatus for coating a plurality of semiconductordevices comprises a mold housing having a formation cavity arranged tohold semiconductor devices. The formation cavity is also arranged sothat a coating material can be injected or otherwise introduced into andfills the formation cavity to at least partially cover the semiconductordevices.

Another embodiment of apparatus according to the present invention isparticularly adapted to coating LEDs and comprises a mold housing havinga formation cavity arranged to hold a plurality of LEDs. The formationcavity comprising at least a top and bottom surface with the LEDsarranged on the bottom or top surface. The mold housing is also arrangedso that a matrix material can be injected into its formation cavitycovering the LEDs and filling the formation cavity.

After the coated LEDs are separated according to the present invention,a bias can be applied to each causing light to be emittedomnidirectionally. LED light passes through the layer of matrix materialwhere at least some of it is converted to a different wavelength oflight by the conversion particles. The arrangement of the formationcavity and the location of cuts between adjacent LEDs allows for thegeometry and thickness of the layer of matrix material on each of theseparated LEDs to be controlled such that the light emitting from theLED at different points on its surface passes through essentially thesame amount of conversion material. This results in an LED with a moreuniform color temperature as a function of viewing angle.

These and other further features and advantages of the invention will beapparent to those skilled in the art from the following detaileddescription, taken together with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of one embodiment of a method for coatingsemiconductor devices according to the present invention;

FIG. 2 is a flow diagram of another embodiment of a method for coatingsemiconductor devices according to the present invention that isparticularly adapted to coating light emitting diodes (LEDs);

FIG. 3 is a sectional view of one embodiment of a coating apparatusaccording to the present invention;

FIG. 4 is a sectional view of the coating apparatus in FIG. 3, with amatrix material injected into the formation cavity;

FIG. 5 is a sectional view of a sheet of LEDs and matrix materialaccording to the present invention;

FIG. 6 is a sectional view of one embodiment of two coated LEDsaccording to the present invention separated from the sheet in FIG. 5;

FIG. 7 is a sectional view another embodiment of two coated LEDsaccording to the present invention separated from the sheet in FIG. 5;

FIG. 8 is a perspective view of one the LEDs shown in FIG. 7;

FIG. 9 is a sectional view of another embodiment of a coating apparatusaccording to the present invention for coating square devices;

FIG. 10 is a sectional view of the coating apparatus in FIG. 9, with amatrix material injected into the formation cavity;

FIG. 11 is a sectional view of a sheet of LEDs and matrix materialaccording to the present invention;

FIG. 12 is a sectional view of one embodiment of two coated LEDsaccording to the present invention separated from the sheet in FIG. 11;

FIG. 13 is a sectional view of another coating apparatus according tothe present invention;

FIG. 14 is a sectional view of the coating apparatus of FIG. 13 with amatrix material injected into the formation cavity;

FIG. 15 is a sectional view of a sheet of LEDs and matrix materialaccording to the present invention;

FIG. 16 is a sectional view of one embodiment of two coated LEDsaccording to the present invention separated from the sheet in FIG. 11;

FIG. 17 is a sectional view of another embodiment of two coated LEDsaccording to the present invention separated from the sheet in FIG. 11;

FIG. 18 is a perspective view of one of the LEDs shown in FIG. 13.

FIG. 19 is a sectional view of another coating apparatus according tothe present invention for coating square devices;

FIG. 20 is a sectional view of the coating apparatus of FIG. 19 with amatrix material injected into the formation cavity;

FIG. 21 is a sectional view of a sheet of LEDs and matrix materialaccording to the present invention; and

FIG. 22 is a sectional view of one embodiment of two coated LEDsaccording to the present invention separated from the sheet in FIG. 11;

DETAILED DESCRIPTION OF THE INVENTION Coating Methods

FIG. 1 shows one embodiment of a method 10 for coating semiconductordevices according to the present invention and comprises a first step 12of providing a mold. A preferred mold comprises a formation cavity thatis arranged so that semiconductor devices can be held within it and acoating material can be injected or otherwise introduced into it tocover the devices. The cavity can have many different shapes and ispreferably defined by at least upper and lower parallel surfaces. Inother embodiments the cavity can be further defined by side surfacesrunning between the upper and lower surfaces. The different shapes ofthe formation cavity including, but are not limited to, disk, box orlens shaped. The side surfaces can run around the entire edge of theupper and lower surfaces or can be intermittent.

In step 14, semiconductor devices are arranged within the formationcavity and in the preferred method 10, the devices are preciselyarranged in a predetermined pattern. The devices can be arranged in manydifferent ways within the formation cavity using many different methods.In a preferred arrangement method the devices are placed on the lowersurface by separating the upper surface from the lower and placing thedevices using a precision pick and place system. Alternatively, thedevices can be placed on the lower surface using a template such as athin metal foil having a size and shape similar to the lower surface andopenings corresponding to desired locations of the semiconductordevices. The foil can be placed on the lower surface and thesemiconductor devices can be arranged within the foil openings. Afterthe devices are placed, the foil can be removed. In both methods theupper surface can then be returned over the lower surface after thedevices are placed. As further described below, the lateral spacebetween adjacent devices and the space between the upper and lowersurfaces provides the desired coating thickness over the semiconductordevices.

In step 16 a coating material is injected or otherwise introduced intothe mold's formation cavity, filling the cavity and covering thesemiconductor devices. In step 18 the coating material is processed andstabilized resulting in the hardening of the coating material and thesemiconductors becoming at least partially embedded in the coatingmaterial. A sheet of semiconductor devices and coating material isformed. In a preferred method 10, the coating material is as an epoxy,silicone or other polymer and the preferred processing and stabilizingstep 18 includes curing using conventional methods dictated by thecoating material's curing schedule. This can include heat curing,optical curing or curing in room temperature. Alternatively, the matrixor coating material may comprise any variety of thermoset, thermoplast,injection molding, or other polymers or related materials.

In step 20, the sheet of semiconductor devices and coating material isremoved from the mold's formation cavity for further processing. In step22 the individual semiconductor devices are separated by cutting throughthe coating material between devices. This can be accomplished usingmany different methods such as conventional sawing or dicing, or byusing a scribe and break.

As described above, in the preferred step 14 the semiconductor devicesare placed on the lower surface with a uniform lateral distance betweenadjacent devices. The upper and lower surfaces of the formation cavityare also preferably parallel. If similar semiconductor devices havingthe same height are placed on the lower surface of the formation cavity,the distance between the top of each of the devices and the uppersurface should be the same. This results in the thickness of the layerof coating material on the top of each of the devices that issubstantially the same. When the devices are separated, the cut ispreferably located such that the resulting layer covering the sides ofeach of the devices has the same thickness. In one embodiment of amethod according to the present invention, the cut is equal distancebetween adjacent devices. This process produces devices that have anearly uniform layer of coating material and the process can be repeatedto produce similar devices. In other embodiments different types of cutscan be made at different angles to change the coating material thicknessat different locations over the semiconductor devices.

The method 10 can be used to coat many different types of semiconductordevices, with a preferred device being a solid state light emitter suchas a light emitting diode (LED). The preferred coating material in themethod for covering LEDs is a “matrix material” that comprises a curablematerial and one or more light conversion materials (further describedbelow).

FIG. 2 shows a flow diagram for a method 30 according to the presentinvention that is similar to the method 10, but is used to coat aplurality of LEDs. In step 32 a mold is provided having a formationcavity having at least upper and lower surfaces that are parallel,although the formation cavity can have many different shapes. The moldsurfaces are preferably flat and comprise a material which does notadhere strongly to matrix materials or the LED during processing stepssuch as curing. By not adhering the upper and lower surfaces can beremoved from the matrix material and LEDs without damage that couldresult in a non-uniform layer of matrix material over the LEDs. Theupper and lower surfaces can be made of by many different materials andcan be provided by sheet metal or glass slides.

To further reduce the danger that the upper and lower surfaces wouldadhere to the matrix material or LEDs, the surfaces of the formationcavity can also be covered with a coating or film layer that resistsadhering to the matrix material and can also withstand heat fromprocessing and curing. The film should be tacky enough on both sides tostick to glass or metal that forms the upper and lower surfaces and tostick to semiconductor materials that form the LEDs. The film should notbond to these materials or the matrix material which allows thesemiconductor devices and cured matrix material to be easily separatedfrom the mold surfaces without damage. Many different films can be usedwith a preferred film being a commercially available tape referred to asGel-Pak®, provided by Gel-Pak, LLC.

In step 34 the LEDs are placed in a predefined array or pattern withinthe mold's formation cavity and in a preferred embodiment the film layeris arranged between the LEDs and the cavity's surface. The LEDs arepreferably arranged on the lower surface of the formation cavity and canbe placed using the same methods as used in step 14 of the method 10described above.

It is desirable to have sufficient adhesion between the LEDs and thesurface of the formation cavity such that underflow of the matrixmaterials is avoided between the LEDs and surface. Lateral LEDs havecontacts on one surface and this surface is typically adjacent to aformation cavity surface (or film layer). Vertical LEDs typically havecontacts on opposite surfaces, both of which can be adjacent to aformation cavity surface. It is desirable to avoid matrix materialunderflow that can cover the contacts so that after processing the LEDcan be electrically contacted. If underflow occurs, the matrix materialmust be removed from the contact surface, typically by etching, whichcan damage the LED and the contacts. One method to improve adhesion andreduce underflow is to apply a small amount of low tack adhesive such assilicone between the LED and the mold surface or film. This additionallayer prevents underflow and can also serve as surface protection forthe contacts during heat processing steps such as curing. Silicone canbe removed by using convention cleaning processes that do not damage theLED or contacts.

In step 36 the matrix material is injected or otherwise introduced intoand fills the mold's cavity, covering the LEDs. The matrix material canbe made of many different compounds but preferably contains one or morelight sensitive conversion materials such as phosphors distributed in anepoxy or silicone binder that can be thermally or optically curable, orcured at room temperature. To achieve uniform LED light emission, theconversion material should be distributed uniformly throughout the epoxyor silicone. For embodiments where it is desirable to emit non-uniformlight, the conversion material can be non-uniform in the matrix materialsuch that LED light emitting at different angles passes throughdifferent amounts of matrix material. Alternatively, the matrix materialmay exhibit or contain materials which exhibit a variety of usefulproperties such as high index of refraction to increase light extractionfrom the LED.

The following is a list of only some of the phosphors and that can beused alone or in combination as the conversion material, grouped by there-emitted color that each emits following excitation.

Red

Y₂O₂S:Eu³⁺, Bi³⁺

YVO4:Eu³⁺, Bi³⁺

SrS:Eu²⁺

SrY₂S₄:Eu²⁺

CaLa₂S₄:Ce³⁺

(Ca,Sr)S:Eu²⁺

Y₂O₃:Eu³⁺, Bi³⁺

Lu₂O₃:Eu³⁺

(Sr_(2-x)La_(x)) (Ce_(1-x)Eu_(x)) O₄

Sr₂Ce_(1-x)Eu_(x)O₄

Sr_(2-x)Eu_(x)CeO₄

Sr₂CeO₄

SrTiO₃:Pr³⁺, Ga³⁺

Orange

SrSiO₃:Eu, Bi

Yellow/Green

YBO₃:Ce³⁺, Tb³⁺

BaMgAl₁₀O₁₇:Eu²⁺, Mn²⁺

(Sr,Ca,Ba) (Al,Ga)₂S₄:Eu²⁺

ZnS:Cu⁺, Al³⁺

LaPO₄:Ce, Tb

Ca,Mg(SiO₄)₄Cl₂:Eu²⁺, Mn²⁺

((Gd,Y,Lu,Se,La,Sm)₃(Al,Ga,In)₅O₁₂:Ce³⁺

((Gd,Y)_(1-x)Sm_(x))₃(Al_(1-y)Ga_(y))₅O₁₂:Ce³⁺

(Y_(1-p-q-r)Gd_(p)Ce_(q)Sm_(r))₃(Al_(1-y)Ga_(y))₅O₁₂

Y₃(Al_(1-s)Ga_(s))₅O₁₂:Ce³⁺

(Y,Ga,La)₃Al₅O₁₂:Ce³⁺

Gd₃In₅O₁₂:Ce³⁺

(Gd,Y)₃Al₅O₁₂:Ce³⁺, Pr³⁺

Ba₂(Mg,Zn)Si₂O₇:Eu²⁺

(Y,Ca,Sr)₃(Al,Ga,Si)₅(O,S)₁₂

Gd_(0.46)Sr_(0.31)Al_(1.23)O_(x)F_(1.38):Eu²⁺ _(0.06)

(Ba_(1-x-y)Sr_(x)Ca_(y))SiO₄:Eu

Ba₂SiO₄:Eu²⁺

Blue

ZnS:Ag, Al

Combined Yellow/Red

Y₃Al₅O₁₂:Ce³⁺, Pr³⁺

White

SrS:Eu²⁺, Ce³⁺, K⁺

It should be understood that many other phosphors and other materialscan be used as the conversion material according to the presentinvention.

From the list above, the following phosphors are preferred for use asthe conversion material based on certain desirable characteristic. Eachis excited in the blue and/or UV emission spectrum, provides a desirablepeak emission, has efficient light conversion, and has acceptable Stokesshift.

Red

Lu₂O₃:Eu³⁺

(Sr_(2-x)La_(x)) (Ce_(1-x)Eu_(x))O₄

Sr₂Ce_(1-x)Eu_(x)O₄

Sr_(2-x)Eu_(x)CeO₄

SrTiO₃:Pr³⁺, Ga³⁺

Yellow/Green

(Sr,Ca,Ba) (Al,Ga)₂S₄:Eu²⁺

Ba₂(Mg,Zn)Si₂O₇:Eu²⁺

Gd_(0.46)Sr_(0.31)Al_(1.23)O_(x)F_(1.38):Eu²⁺ _(0.06)

(Ba_(1-x-y)Sr_(x)Ca_(y)) SiO₄:Eu

Ba₂SiO₄:Eu²⁺

To further improve the uniformity of light emission from the coveredLED, the matrix material can also include scattering particles torandomly refract the light as it passes through the matrix material. Toeffectively scatter light, the diameter of the scattering particlesshould be approximately one half of the wavelength of the light beingscattered. Light from the LEDs pass through the particles and isrefracted to mix and spread the light. Preferred scattering particles donot substantially absorb LED light and have a substantially differentindex of refraction than the material in which it is embedded (forexample, epoxy). The scattering particles should have as high of anindex of refraction as possible. Suitable scattering particles can bemade of titanium oxide (TiO₂) which has a high index of refraction(n=2.6 to 2.9). Other elements such as small voids or pores could alsobe used as to scatter the light.

In step 38, the matrix material is cured such that the LEDs are at leastpartially embedded in the matrix material. In the embodiment where theformation cavity comprises parallel upper and lower surfaces, LEDs andmatrix material form a sheet with the LEDs at least partially embeddedin the matrix material. The matrix material is allowed to cure by thematerial's curing schedule either in room temperature, under light foroptical curing, or at an elevated temperature for heat curing. In apreferred embodiment of the method 30, all surfaces of the LEDs arecovered except for their bottom surface. In step 40 the sheet of LEDsand matrix material is removed from the molds formation cavity, with onemethod being separating the upper and lower surfaces of the mold torelease the sheet, although many other methods can also be used. In step42, each LED can be singulated, preferably by separating the LEDs in thesheet into individual devices each of which has a similar thickness ofmatrix material around it. The methods described under step 20 of method10 can be used, including sawing or dicing or scribe-and-break.

The mold is designed such that the distance between the formationcavity's upper and lower surfaces and the lateral separation betweenadjacent LEDs results in the desired uniform matrix material thicknesson each of the separated LEDs. This results in coated LEDs that emituniform color temperature and LEDs that can be consistently reproducedwith the same or similar emission characteristics.

As more fully described below, depending on the type of LED beingcoated, the mold can be arranged differently. For lateral devices, whereboth the positive and negative terminals are on the same LED surface,the LEDs can be arranged with the contacts adjacent to the cavity'slower surface. Spacers can be included between the upper and lowersurfaces to maintain the desired distance between the two such thatthere is a space between the top of the LEDs and the upper surface ofthe formation cavity. When the cavity is filled with the matrixmaterial, that top surface of each of the LEDs is covered by a layer ofmatrix material having a similar thickness.

For LEDs having vertical contact geometry, one contact can be on eachLED's top surface and the other contact can be on the LED's bottomsurface. The top contact terminal should be protected during injectionof the matrix material so that it is not covered by the matrix material.In one embodiment, the cavity's upper surface rests on the top surfacecontacts of the LEDs, with the contact point between the two preventingthe top contacts from being fully covered by the injected matrixmaterial.

For each of the above methods, the mold's formation cavity can beprovided without a top surface. In those embodiments the matrix shouldbe applied carefully and in a more controlled fashion to proved thedesired thickness for the top layer in lateral LEDs and to preventcovering the top contact surface in vertical LEDs.

Coating Apparatus

FIGS. 3 and 4 show one embodiment of a compact coating apparatus 50according to the present invention that can be used to compact coat manydifferent semiconductor devices, but is particularly adapted to compactcoating lateral LEDs with a matrix material. The apparatus 50 includes amold housing 51 comprising a lower section 52 that includes a bottomrigid support block 54 having LEDs 55 arranged on its top surface. Thetop surface 56 the bottom support block 54 is preferably flat and theblock 54 can be made of many different materials with many differentthicknesses. The block material should not adhere to the LED or matrixmaterial during the curing process. Suitable materials include aluminum,glass and stainless steel, and the bottom support block 54 should bethick enough that it does not flex during the layer formation process.

The LEDs 55 can be placed on the support block using the precisionplacement methods described above. A double sided adhesive film 58 canalso be included between the LEDs 55 and the bottom block's flat surface56. As described above, the film 58 sticks to the block surface 56 andalso provides a tacky surface that holds the LEDs 55. The film 58 alsowithstands processing and curing steps while not adhering to the matrixmaterial, with a suitable material for film 58 being Gel-Pak® (describedabove in the method 10 of FIG. 1). The film 58 helps to reduce theamount of matrix material that sticks to the surface of the bottomsupport block 54. In the embodiment shown with lateral LEDs 55, thepositive and negative terminals 59, 60 for each of the LEDs 55 are onthe surface of each LED that is adjacent to the first film 58 so thatwhen the matrix material is injected into the mold 50, the positive andnegative terminals are not covered by the matrix material.

The mold housing 50 also includes an upper section 61 arranged over thelower section 52. The upper section 61 comprises a top rigid supportblock 62 that provides a flat top surface 64 and can be made of the samematerial with the same or different thickness as the bottom rigidsupport block 54. A second layer of adhesive film 63 can also beincluded on the flat top surface 64 to provide a surface that doesresists adhesion to the matrix material, and withstands the processingand curing steps.

The upper section 61 is arranged over the lower section 52 with thespace between the two at least partially defining the mold's formationcavity 68. The space between the two should be large enough to provide aspace between the top of the LEDs 55 and the second adhesive film 63.Referring to FIG. 4, a matrix material 70 can be injected or otherwiseintroduced into the formation cavity 68 such that it fills the spacebetween the upper and lower section 52 and 61 and each of the LEDs iscovered by the matrix material 70. The positive and negative terminals59, 60 are protected from being covered by the matrix material and afterthe individual LEDs are separated (singulated) the terminals 59, 60 areavailable for contacting.

During the injection of the matrix material 70 and subsequentprocessing/curing steps, the distance between the lower and uppersections 52 and 61 should be maintained. The lower and upper sections 52and 61 can have first and second vertical spacers 65, 66 (shown in FIGS.2 and 4) running between them. The spacers 65, 66 are arranged tomaintain the distance between the lower and upper sections 52 and 61 sothat the desired matrix material layer thickness is achieved on the topsurface of the LEDs 54. The spacers 65, 66 can be arranged in manydifferent ways and can be formed as a single spacer around the edge ofthe entire formation cavity 68, or multiple spacers can be used.

The inside surfaces of the spacers 65, 66 further define the formationcavity 68 into which the matrix material 70 is injected. The matrixmaterial 70 can be injected or introduced into the cavity 68 by manydifferent methods according to the present invention. One such methodcomprises removing the upper section 61, injecting the material 70 intothe cavity using a syringe, and replacing the upper section 61.Alternatively, the mold 50 can have an access opening through one of itsrigid blocks 54, 62 or through one its spacers 65, 66 so that the matrixmaterial 70 can be injected into the cavity without removing either thelower and upper sections 52, 61 or one of the spacers 65, 66. The matrixmaterial 70 can be made of the same material as described in step 36 ofthe method 30 above and preferably comprises phosphor conversionparticles of one or more different type distributed uniformly throughouta curable epoxy, silicone or other polymer.

After the matrix material 70 is injected into the formation cavity 68,the matrix material 70 is cured using a process dictated by the type ofepoxy or silicone such as heat curing, light curing or room temperaturecooling. After the curing process is complete the matrix material 70 andLEDs 55 form a sheet that can be removed from the mold's formationcavity 68 by removing one or both of the lower and upper sections 52,61, and/or one or both of the spacers 65, 66.

FIG. 5 shows a sheet 72 of matrix material 70 and LEDs 55 after it isremoved from the formation cavity 68 of the mold apparatus 50. The sheetcan now be separated into individual coated LEDs by sawing, dicing orusing a scribe and break.

FIG. 6 shows two coated LEDs 76 separated from the sheet 72 shown inFIG. 5. In the embodiment shown, each of the coated LEDs 76 is separatedby making vertical cuts through the matrix material between adjacentLEDs 55. The matrix material can be cut in many different ways such thatthe layer has different thickness over the LEDs 55 or different LEDs 55cut from the same sheets can have layers with different thicknesses. Thecoated LEDs 76 shown in FIG. 6 are cube shaped and the matrix materialcut is preferably made at a midpoint between adjacent LEDs 55 so thatthe side thickness of the matrix material on each coated LED 76 is thesame. In other embodiments the cut can be made off midpoint or two cutscan be made, each of which is off midpoint but closer to one of theadjacent LEDs 55 such that the side thickness of the matrix material isstill the same for each LED. This type of cubed shaped arrangement isparticularly applicable to LEDs that are square, although it can also beused with LEDs having angled surfaces as shown.

For different shaped LEDs, the matrix material can also be cut so thatthe matrix material layer conforms to the shape of the LED. FIGS. 7 and8 show individually coated angled side surface coated LEDs 79 that havea layer of matrix material 80 that more closely conforms to the shape ofeach LED 55. Angled side surfaces are typically included to increase theLEDs light extraction. The shape of the matrix layer 80 can be obtainedusing different methods, with a preferred method being cutting throughthe matrix material to a depth 84 using a wider sawing (dicing) bladehaving an angled point. The remainder of the matrix material can then becut using a standard narrow sawing (dicing) blade. The layer 80 conformsmore closely to the shape of the LED such that light emitting from theLED 55 passes through substantially the same amount of matrix material.Accordingly, light emitted from the coated LED 79 is more uniform andtotal internal reflection is reduced. Each of the coated LEDs 79 haveboth contacts on the bottom, uncoated surface 86 and FIG. 8 also showsfirst and second conductors 88, 89 that can be used to apply a biasacross the contacts, causing the LED 55 to emit light.

FIGS. 9 and 10 show another embodiment of a compact coating apparatus 90according to the present invention that comprises many of the samefeatures as the apparatus 50 shown in FIGS. 3 and 4, with the apparatus90 used to coat square LEDs 92. The features of the apparatus 90 thatare the same as those in the apparatus 50 use the same referencenumerals in FIGS. 9 and 10. Accordingly, the reference numerals and manyof the corresponding features are not introduced or described again inthe referring to FIGS. 9 and 10.

Like the LEDs 55 in FIGS. 3 and 4, the square LEDs 92 are arranged oneither the top surface 56 of the support block 54, or in the embodimentshown with a first film 58, on the top surface of the adhesive film 58such that portions of the film are sandwiched between the LEDs 92 andthe support block 54. The LEDs 92 have bottom contacts 93 whose topsurface is protected by the block 54 or film 58 from being covered bythe matrix material. Referring to FIG. 10, a matrix material 94 can beinjected into the formation cavity 68 covering the LEDs 92 and thematrix material 94 can be cured such that the LEDs 92 become embedded inthe matrix material 94.

FIG. 11 shows the sheet 96 of LEDs 92 and matrix material 94 after beingremoved from the formation cavity by the methods described during thediscussion of FIGS. 4 and 5 above. FIG. 12 shows the individual coatedLEDs 98 after being separated from the sheet 96 using the separationmethods described above, with each of the square LEDs 92 having a nearlyuniform layer of matrix material 94 so that the coated LEDs 98 emitsimilar light.

FIG. 13 shows another embodiment of a mold apparatus 100 that can alsobe used to compact coat different semiconductor devices, but isparticularly adapted to coating semiconductor devices that have acontact on their top surface. One such device is a vertical LED 102having a first contact 103 on its bottom surface and a second contact104 on its top surface. The apparatus 100 comprises a mold housing 101including a lower section 106 that is similar to the lower section 54described in FIG. 3, and comprises a bottom support block 108 and afirst double sided adhesive film 110 (e.g. Gel-Pak®). Vertical LEDs 102are arranged on the layer 110 with their first contact 103 adjacent tothe layer 110.

The apparatus 100 also comprises an upper section 112 that is similar tothe upper section 61 described in FIGS. 3 and 4, and comprises a toprigid block 114 and a second double sided adhesive film 116. However, inapparatus 100 there are no spacers. Instead, the second adhesive film116 rests on the second contacts 104 of the LEDs 102, which maintainsthe appropriate distance between the lower and upper sections 106, 112and also protects the top of the contacts 94 from being covered by thematrix material. If desired, the apparatus 100 can include side surfaces(not shown) to further define the formation cavity 119.

FIG. 14 shows the apparatus 100 with the matrix material 118 injected orotherwise introduced between the lower and upper sections 106, 112, thatat least partially define a formation cavity 119. The matrix material118 can then be cured using the processes described above, so that theLEDs 102 and matrix material 118 form a sheet 120. The first contact 103of each LED 102 is protected from being covered by the matrix material118 by the first adhesive film 110 and second contact 104 is protectedfrom being fully covered by the matrix material by the second adhesivefilm 116. Accordingly, both the first and second contacts 103, 104 areavailable for electrical contact without further processing or etching.

FIG. 15 shows the sheet 120 after it has been removed from the apparatus100. FIG. 16 shows individual coated LEDs 122 after they have beenseparated, with the preferred separation method being vertical cutsthrough the matrix material between adjacent LEDs 102 to form cubeshaped devices. FIGS. 17 and 16 show LEDs 123 after being cut to matchthe angled sides of the LEDs 92. This can be accomplished using the twocut method described above wherein a wider saw with and angled blade isused to cut the matrix material to a first depth 124 and a standardnarrower blade is used to cut through the remainder of the matrixmaterial. FIG. 18 shows the second contact 104 available for contactingwith a first conductor 128 coupled to the second contact 104. A bottomconductor 129 is coupled to the LED's first contact 103 (shown in FIG.17). A bias applied across conductors 128 and 129 causes the coated LED102 to emit light.

FIGS. 19 and 20 show another embodiment of a compact coating apparatus130 according to the present invention that comprises many of the samefeatures as the apparatus 100 shown in FIGS. 13 and 14, with theapparatus 130 used to coat square LEDs 132. The features of theapparatus 130 in FIGS. 19 and 20 that are the same as those in theapparatus 100 in FIGS. 13 and 14 use the same reference numerals for thesame features. Accordingly, the reference numerals and many of thecorresponding features are not introduced or described again in thereferring to FIGS. 19 and 20.

Like the LEDs 102 in FIGS. 13 and 14, the square LEDs 132 have a firstcontact 133 and a second contact 134 and the LEDs 132 are arranged oneither the top surface of the block 108, or in the embodiment shown witha first film 110, on the top surface of the adhesive film 110. Portionsof the film 110 are sandwiched between the LEDs 132 and the block 108,with their first contacts 133 protected. The upper section 112 isarranged on the LEDs second contacts 134 such that they are alsoprotected.

Referring to FIG. 20, a matrix material 136 can be injected or otherwiseintroduced into the formation cavity covering the LEDs 123 and thematrix material 136 can be cured such that the LEDs 132 become embeddedin the matrix material 136.

FIG. 21 shows the sheet 138 of LEDs 132 and matrix material 136 afterbeing removed from the formation cavity by the methods described in thediscussion of FIGS. 4 and 5 above. FIG. 22 shows the individual coatedLEDs 139 after being separated from the sheet 138 using the methodsdescribed above in the discussion of FIGS. 6, 7 and 8. Each of thesquare LEDs 132 has a similar layer of matrix material 136 so that theLEDs 132 emit similar light.

Each of the apparatus described above can include a small amount of lowtack adhesive such as silicone between the LED contacts and the moldsurface or film as described in the method 10 of FIG. 1. As describedabove, this additional layer prevents underflow and can also serve assurface protection for the contacts during heat processing steps such ascuring. Silicone can then be removed by using convention cleaningprocesses that do not damage the LED or contacts.

Although the present invention has been described in considerable detailwith reference to certain preferred configurations thereof, otherversions are possible. Different curable materials and light conversionparticles can be used. The molds can take different shapes, can havedifferent components and the semiconductor devices can be arrangeddifferently in the mold's formation cavity. The individual LEDs can beseparated from the sheet using many different sawing or dicing methods,with the cuts being straight or angled through the matrix material. Thedifferent coating apparatus described above can be provided without anupper section and in those embodiments the matrix material should beintroduced in a careful and controlled manner to provide the desiredlayer of matrix material. Therefore, the spirit and scope of theappended claims should not be limited to their preferred versionscontained therein.

We claim:
 1. A light emitting diode (LED), comprising: a plurality ofsemiconductor layers comprising an active region between two oppositelydoped layers; positive and negative contacts on the same surface of saidsemiconductor layers and coplanar with each other, said active regionemitting light in response to an electrical signal applied to saidcontacts; and a conformal coat of matrix material covering surfaces ofsaid semiconductor layers, with an exposed portion of each of saidcontacts being uncovered by said matrix material and coplanar with anadjacent surface of said matrix material.
 2. The LED of claim 1, whereinsaid contacts are accessible from the bottom of said semiconductorlayers.
 3. The LED of claim 1, wherein said matrix material comprisesone or more phosphors.
 4. The LED of claim 1, wherein said matrixmaterial comprises one or more phosphors distributed in a binder.
 5. TheLED of claim 1, wherein said active region light passes through saidmatrix material wherein at least some of said active region light isconverted to a different wavelength by said matrix material.
 6. The LEDof claim 1, wherein said active region light comprises blue or UV light,and said matrix material absorbs at least some of said active regionlight and re-emits light at a different wavelength.
 7. The LED of claim6, wherein said matrix material re-emits yellow or green light.
 8. TheLED of claim 1, wherein said semiconductor layers further compriseshaped side surfaces, wherein said matrix material conforms to saidshaped side surfaces.
 9. The LED of claim 1, wherein said semiconductorlayers further comprise top and side surfaces, wherein said matrixmaterial covers at least some of said top and side surfaces.
 10. The LEDof claim 1, wherein said matrix material further comprises scatteringparticles.
 11. The LED of claim 1, wherein at least some of said activeregion light passes through said matrix material, said matrix materialsuch that said active region light passes through substantially the sameamount of matrix material.
 12. A light emitting diode (LED), comprising:a plurality of semiconductor layers in a lateral geometry; positive andnegative terminals on the same side of said semiconductor layers andcoplanar with each other, said semiconductor layers emitting light inresponse to an electrical signal applied to said terminals; and aconformal coat of conversion material covering surfaces of saidsemiconductor layers, said conversion material converting at least someof said semiconductor layer light, with an exposed portion of each ofsaid terminals being uncovered by said conversion material and coplanarwith an adjacent surface of said conversion material.
 13. The LED ofclaim 12, wherein at least a portion of said terminals being uncoveredby said matrix material.
 14. The LED of claim 12, said LED comprisingangled side surfaces to increase light extraction.
 15. The LED of claim12, wherein said semiconductor layers have a top and side surfacescovered by said conversion material.
 16. The LED of claim 15, whereinsaid semiconductor layer light passes through substantially the sameamount of conversion material.
 17. The LED of claim 15, wherein saidterminals are accessible from the bottom of said semiconductor layers.18. The LED of claim 15, wherein said conversion material comprises oneor more phosphors distributed in a binder.
 19. The LED of claim 18,wherein said conversion material is distributed uniformly in saidbinder.
 20. The LED of claim 18, wherein said conversion material isdistributed non-uniformly in said binder.
 21. The LED of claim 1,wherein said semiconductor layer light comprises blue or UV light, andconversion material absorbs at least some of said semiconductor layerlight and re-emits light at a different wavelength.
 22. The LED of claim6, wherein said conversion material re-emits yellow or green light. 23.A light emitting diode (LED), comprising: semiconductor layers; contactson said semiconductor layers on the same surface of said semiconductorlayers and coplanar with each other; a conversion material as aconformal coat on said semiconductor layers, with an exposed portion ofeach of said contacts being uncovered by said conversion material andcoplanar with an adjacent surface of said conversion material.
 24. TheLED of claim 23, wherein said semiconductor layers further comprise topand bottom surfaces, conversion material covering at least a portion ofsaid semiconductor layers top and side surfaces.
 25. The LED of claim23, wherein said contacts are accessible from the bottom surface. 26.The LED of claim 23, wherein said semiconductor layers are in a lateralgeometry.